The present invention relates generally to ink, and more particularly to printing ink for use with a recording device such as a printer.
The ink of the present invention is preferably applicable to a piezo-type inkjet head in which a piezoelectric element is used for a print head or a film-boiling-type (or bubble-type) inkjet head, and can widely be employed not only for a printer (inkjet printer) as a single unit, but also for a copier, a facsimile, a computer system, word-processor, or the combination thereof which has a printing function.
The inkjet printer is currently in increasing demand due to its excellence in noiseless operation and easiness to achieve a fall-color printing. In particular, the drop-on-demand inkjet head that ejects ink droplets from an inkjet nozzle only when necessary in printing operation has become widely used.
Among inkjet heads, those using a piezoelectric element (i.e. piezo-type inkjet head) have increasingly come into the limelight in recent years for their high energy-efficiency, etc. This kind of inkjet head typically includes a piezoelectric element, one common ink chamber which receives from an external device and stores ink, a plurality of pressure chambers connected to the piezoelectric element and a nozzle plate connected to the pressure chambers so that a nozzle may be connected to each pressure chamber. Each pressure chamber is connected to the common ink chamber through an ink supply channel so that it may receive ink from the common ink chamber and increase an internal pressure by utilizing a deformation of the piezoelectric element, thereby ejecting ink from each nozzle.
Other than the piezo-type inkjet head, those which eject ink droplets by using so-called bubble-type (film-boiling-type) ink ejecting means are known too.
Conventionally, the ink employed for this kind of inkjet recoding device is basically composed of a dye and a water-soluble organic solvent, but the dye has the intrinsic disadvantages of low water resistance and inferior lightfastness. Thus, to overcome such disadvantages, aqueous dispersoid ink (or pigment ink), which uses a pigment instead of a dye, has been developed. Compared with the dye ink, the aqueous dispersoid ink (or pigment ink) has a number of advantages in high water resistant lightfast property, high optical density on a recording medium, and less blurred property, etc.
The pigment ink, however, is disadvantageously difficult to keep a pigment particle stable because the pigment itself is insoluble in water or other solvents, and likely to clog in the nozzle. Accordingly, securing the ink dispersive stability has posed the most significant challenge in the pigment ink. Various proposals have been made to deal with this challenge, but prior art proposals have been found still insufficient.
For example, seeking to provide the dispersive and preservative stabilities to writing ink for use with a pen, etc. comprising a pigment, a dispersing agent, and an aqueous medium, Japanese Patent Publication (Kokai) No. 55-35434 has proposed to employ as a dispersing agent a polymer including as a main constituent alkyl ester of acrylic or methacrylic acid sharing both hydrophilic and lipophilic portions, and to employ an aqueous medium including a nonvolatile hydrophilic organic solvent, such as ethylene glycol.
However, writing ink is intrinsically unfit for ink used for such an inkjet recording device as ejects a droplet from a micro nozzle (hereinafter referred to as xe2x80x9cinkjet inkxe2x80x9d), and a long-term conservation thereof would evaporate water, increase its viscosity, and flocculate its particle; therefore such writing ink cannot be considered to secure the dispersive and preservative stabilities to such an extent as to be satisfactorily applicable to inkjet ink.
Accordingly, it is an exemplified general object of the present invention to provide novel and useful ink, an ink storage such as an ink cartridge or tank, and a recording device using the ink in which the above disadvantages are eliminated.
More specifically, it is an exemplified object of the present invention to provide such ink that maintains the dispersive and preservative stabilities fit for inkjet ink, an ink storage, and a recording device using the ink.
The present inventors, after thorough study to achieve the above objects, have discovered that the previous disadvantages may be eliminated by instant novel dispersoid ink including a specific pigment, dispersing agent and/or additive in which a dispersed particle in the ink ranges in average diameter within a specific range when measured on a specific principle by a specific detection process.
Ink set forth in claim 1 comprises water and a water-soluble organic solvent, wherein a dispersed particle included in the ink further comprises a colorant including at least a carbon black, wherein the dispersed particle has a primary particle diameter of 30 nm or smaller, a BET specific surface area of 200 m2/g or smaller, a DBP oil absorption amount of 80 cc/100 g or smaller, a volatilization rate of 2.0% or higher, and a pH not greater than 7, and wherein the ink further comprises as a dispersing agent an acrylic macromolecule copolymer having weight average molecular weight of 80,000 or less. A relatively small primary particle, that is 30 nm or smaller in diameter, of the dispersed particle is selected so that it may hardly be precipitated. The dispersed particle if having the BET specific surface area of 200 m2/g or smaller would not be porous in general. The DBP oil absorption amount of 80 cc/100 g or smaller indicates the dispersed particle is relatively not so flocculated. The carbon black having a volatilization rate of 2.0% means that the dispersed particle has an oxidized film, etc. A pH not greater than 7 indicates that the dispersed particle is acidized. The present inventors have discovered that the ink satisfying these requirements is stable dispersoid ink. Moreover, the inventers have discovered that the ink further comprising as a dispersing agent an acrylic macromolecule copolymer having weight average molecular weight of 80,000 or less may gain further improved stability.
The ink set forth in claim 2 comprises water and a water-soluble organic solvent, wherein a dispersed particle included in the ink further comprises a colorant including at least a carbon black, wherein the dispersed particle has a primary particle diameter of 30 nm or smaller, a BET specific surface area of 200 m2/g or smaller, a DBP oil absorption amount of 80 cc/100 g or smaller, a volatilization rate of 2.0% or higher, and a pH not greater than 7, wherein the ink further comprises as a dispersing agent a polymer indispensably including hydrophilic, cationic and lipophilic components. The dispersed particle having a primary particle larger than 30 nm, a BET specific surface area larger than 200 m2/g, a DBP oil absorption amount larger than 80 cc/100 g, a volatilization rate lower than 2.0%, and a pH greater than 7 would easily be flocculated and make its dispersion unstable. The present inventors have discovered that the ink further comprising as a dispersing agent a polymer indispensably including hydrophilic, cationic and lipophilic components in addition to these requirements may have further improved stability.
Because the carbon black carries negative charge, and, when the above dispersing agent is employed, the dispersing agent is adsorbed with its lipophilic component and adhered with its cationic component to a surface of the pigment, and the hydrophilic portion is dissolved in an aqueous medium. It is conceivable that a pigment particle is stably retained in the aqueous medium by the action of these three portions of the dispersing agent.
The ink set forth in claim 3 is aqueous dispersoid ink comprising at least water, a water-soluble organic solvent, and a colorant, wherein a ratio R of Kt to Ko (=Kt/Ko) satisfies Rxe2x89xa65 where Ko (=Dm/Do) is a ratio of a maximum particle diameter Dm to an average particle diameter Do in said ink, both of which diameters are measured by detecting backscattering light and converting a detection result into a particle diameter under a dynamic light scattering method as a measurement principle, and Kt (=Tm/To) is a ratio of a maximum particle diameter Tm to an average particle diameter To in said ink that has been preserved for six months at a constant temperature of 50xc2x0 C., both of which diameters are measured by the above principle and detection method. If R amounted to five or more, a maximum-to-average particle diameter ratio (size) would be five times larger than that in its initial state, which indicates that the dispersed particle (particularly the maximum particle) in the ink would rapidly grow. In such ink, a dispersed particle would have a propensity to become flocculated for a long period over time, and also have an increasing possibility to be precipitated. There would be a good possibility that a disperse system of such ink would become unstable, and a preservative stability would be damaged.
According to the ink set forth in claim 4 that depends upon claim 3, an average particle diameter To of the dispersed particle included in the ink that has been preserved for six month at a constant temperature of 50xc2x0 C. and then measured by applying the above principle and detection method ranges 10 nmxe2x89xa6Toxe2x89xa61,000 nm, and satisfies Doxe2x89xa6To. The ink which satisfies 10 nmxe2x89xa6Toxe2x89xa61,000 nm and Doxe2x89xa6To may provide a more stable disperse system compared with the ink claimed in claim 3. This is because To over 1,000 nm may produce a clog in the nozzle of the inkjet recording device, and considerably damage its reliability. In addition, it is practically impossible to consistently produce a particle having a diameter smaller than 10 nm. To is an average particle diameter after a change over time from an initial value, and is generally larger than the initial value Do.
According to the ink set forth in claim 5 that depends upon claim 3, a maximum particle diameter Tm of the dispersed particle included in the ink that has been preserved for six months at a constant temperature of 50xc2x0 C. and then measured by applying the above principle and detection method ranges 10 nmxe2x89xa6Tmxe2x89xa610,000 nm and satisfies Dmxe2x89xa6Tm. The ink which satisfies 10 nmxe2x89xa6Tmxe2x89xa610,000 nm and Dmxe2x89xa6Tm may provide a more stable disperse system compared with the ink claimed in claim 3. This is because To over 1,000 nm may produce a clog in a nozzle of an inkjet recording device, and considerably damage its reliability. In addition, it is practically impossible to consistently produce a particle having a diameter smaller than 10 nm. To is an average particle diameter after a change over time from its initial value, and is generally larger than an initial value Do.
The ink set forth in claim 6 that depends upon claim 3 is filtrated with a filter whose pore size Df satisfies 1 less than Df/Dmxe2x89xa64. Df is the minimum pore size through which the particles may be filtrated in whole (pass by 100%). Taking it into consideration that a selection of the filter pore size based on a value measured by a particle analyzer may cause an unsuccessful filtration, the ink is limited to that which can pass through a filter with a specific range of pore size.
The ink set forth in claim 7 that depends upon claim 6 has a filter whose material is selected from a group consisting of cellulose acetate, cellulose nitrate, regenerated cellulose, polysulfone, polypropylene, and polyamide, and a combination thereof. The usable filter materials to ease the filtration of the ink may be hydrophilic ones.
According to the ink set forth in claim 8 that depends upon claim 3, the dispersed particle comprises a colorant including at least a carbon black, and has a primary particle diameter of 30 nm or smaller, a BET specific surface area of 200 m2/g or smaller, a DBP oil absorption amount of 80 cc/100 g or smaller, a volatilization rate of 2.0% or higher, and a pH not greater than 7. Because the dispersed particle having a primary particle diameter larger than 30 nm, a BET specific surface area larger than 200 m2/g, a DBP oil absorption amount larger than 80 cc/100 g, a volatilization rate lower than 2.0%, or a pH greater than 7 may easily be flocculated in the dispersoid ink, and destabilize the dispersion.
The ink set forth in claim 9 that depends upon claim 3 further comprises a dispersing agent. The dispersing agent may increase ink""s dispersive stability.
The ink set forth in claim 10 that depends upon claim 9 may comprises a dispersing agent that is an acrylic macromolecule copolymer having a weight average molecular weight of 80,000 or less. The inventors have discovered that such ink is excellent in stability.
The ink set forth in claim 11 that depends upon claim 9 comprises a dispersing agent that is a polymer indispensably including hydrophilic, cationic and lipophilic components. Such ink is more excellent in stability than that claimed in claim 9. Because the carbon black carries negative charge in the aqueous solvent, and, when the above pigment is employed, the dispersing agent is adsorbed with its lipophilic component and adhered with its cationic component to a surface of the pigment, and the hydrophilic portion is dissolved in an aqueous medium. It is conceivable that a pigment particle is stably retained in the aqueous medium by the action of these three portions of the dispersing agent.
According to the ink set forth in claim 12 that depends upon claim 3, its viscosity xcex7 at 20xc2x0 C. satisfies 1 cPxe2x89xa6xcex7xe2x89xa6100 cP. The inventors have discovered that such ink is excellent in stability.
The claims 13 through 16 disclose the ink storage and the recording device that use the above ink. Since they use the ink that is excellent in dispersion and preservative stability, they provide a stable recording operation without clogs and high printing quality.
The ink set forth in claim 17 comprises at least water, a water-soluble organic solvent, and a colorant, wherein a ratio R of Kt to Ko (=Kt/Ko) satisfies Rxe2x89xa65 where Ko (=Dm/Do) is a ratio of a maximum particle diameter Dm to an average particle diameter Do if the diameter of a dispersed particle included in the ink is measured directly, and Kt (=Tm/To) is a ratio of a maximum particle diameter Tm to an average particle diameter To if the diameter of a dispersed particle included in the ink that has been preserved for six months at a constant temperature of 50xc2x0 C. and then measured.
Other objects and further features of the present invention will become readily apparent from the following description and accompanying drawings.